Title

Author

Defense Date

2007

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Biomedical Engineering

First Advisor

Dr. Gary L. Bowlin

Abstract

Traumatic defects in articular cartilage can lead to joint disease and disability including osteoarthritis. Because cartilage is unable to regenerate when injured, the field of tissue engineering holds promise in restoring functional tissue. In this research, type II collagen was electrospun, cross-linked, and tested as scaffolds for supporting chondrocyte growth. The mechanical, biochemical, and histological characteristics of the engineered tissue were assessed as a function of the electrospinning solution concentration (i.e. scaffold fiber diameter and pore properties) and as a function of the time in culture (evaluated at 2, 4, and 6 weeks). Fiber diameter had a linear relationship with concentration: mean diameter increased from 107 to 446 nm and from 289 to 618 nm, measured with SEM and permeability meter, respectively, with increasing concentration, from 60 mg/mL to 120 mg/mL. Pore size revealed no relationship with concentration but mean values ranged in size from 1.76 to 3.17 μ2 or from 0.00055 to 0.0028 μ2, depending on the measurement technique. Average porosity ranged from 84.1 to 89.1%, and average permeability was between 6.82x10-4 and 35.0 x10-4 D. Histological analysis revealed a relatively high number of spherical cells, possibly indicating the expression of the chondrocyte phenotype. However, there were very little glycosaminoglycans and type II collagen synthesized by the cells despite an increase in the cell density over time for the 60, 80, and 100 mg/mL concentrations. The mean values for peak stress (between 0.17 and 0.35 MPa) and tangential modulus (between 0.32 and 0.64 MPa) for the mats are at least an order of magnitude less than that for native cartilage, while the mean values for strain at break (between 93 and 150%) for the mats are at least an order of magnitude greater than that for native cartilage. The equilibrium stiffness for all concentrations decreased from week 2 to week 6 of tissue culture (which may correlate with increasing cell density); the 100 mg/mL concentration had the highest mean value (0.084 MPa at week 2) and the lowest mean value (0.010 MPa at week 6). This research did not indicate any significant findings regarding the influence of concentration or culture time on chondrogenesis. Because the cells appeared to grow on the surface of the scaffold but there was a lack of cell migration into the scaffold, the scaffold material may be sufficient to support chondrocyte growth but the scaffold physical design must be reconsidered.